Savage I can not post a screen shot but I am doing as you direct the problem is the slider goes white from the bottom and black from the top. the slider is moving in its entirely as pulled down it doesn't reduce in size but just repeats black to white.

Yes, move the ends of the curly bracket, not the grey - scale? Although the mouse pointer does not modify itself to show you this is possible, just have faith and put it over the end of the bracket and drag up and down.

Image 1 shows an enlarged example of where precisely you should put your pointer before holding down the left mouse button to drag the end of the curly bracket. Helpful?

Edit. Tip - if your cursor transforms into a double headed arrow pointing up and down. Then you have got hold of the wrong thing.